1. Field of the Invention
The present invention relates to a heat generating bag for footwear using a sheet shaped heat generating body, and more particularly to a thin heat generating bag having high heat generating performance and inside which the heat generating composition is not displaced.
2. Disclosure of the Related Art
Conventionally, heat generating bags wherein an air-permeable bag containing a heat generating composition with oxidizable metals such as iron powder as the prinicipal component, and emit heat upon contact with oxygen in the air, have been widely used as pocket heaters. In Utility Model Laid-Open (Kokai) Publication No. SHO 59-071618, an air-permeable heat generating bag in the shape of a horseshoe or a trapezoid which is used as a heat generating bag etc. for shoes or slippers is disclosed.
All of these heat generating bag for footwear are air-permeable bags containing moist powder which is a mixture of iron powder, activated carbon, a water holding agent, an inorganic electrolyte etc. These heat generating bag for footwear are sealed in a non-air permeable bag and kept there until they are used. Upon use, the outer bag is torn, and the heat generating bag for footwear is taken out for application and use inside a footwear.
However, conventional heat generating bag for footwear were inconvenient in that, upon use inside a pair of shoes, the bag would be warm and comfortable only when the wearer stayed still, but the temperature of the heat generating bag for footwear would suddenly rise and become too hot when the wearer walked. In contrast, when the heat generating temperature of the bag was set at a substantially low temperature to secure a comfortable temperature upon walking, insufficient heat was obtained when staying still.
Moreover, conventional heat generating bag for footwear were inconvenient in that, upon application inside a pair of shoes, they would be twisted or their heat generating composition powder would be displaced to one side during use and cause an uncomfortable feeling to the wearer. Furthermore, if a heat generating bag was used with such heat generating composition remaining at one side, limited portions where the heat generating composition concentrated occasionally showed high temperatures.
Under these circumstances, there has been a demand for a development of a heat generating bag for footwear which provides a comfortable temperature regardless of the state of use, which is thin, avoids uncomfortableness of the wearer, and is easily manufactured.